It is known to form solid golf balls by covering a solid polybutadiene rubber core with a thermal plastic resin cover. Solid golf balls having a cover of ionomer-base material have superior durability and good flight performance. Unfortunately, in comparison with a thread wound golf ball, a solid golf ball is more difficult to control, particularly when the ball is struck with a middle or iron. Additionally, the solid golf ball has an undesirable "feel" upon striking, due to the relative hardness of the cover. For this reason, most professional golfers do not use solid golf balls in tournaments. Previous attempts to improve the "feel" of conventional solid golf balls have focused on lowering the hardness of the solid core and forming the cover of softer material. Neither of the solutions has proven satisfactory because they sacrifice flight performance and durability.
Thread wound golf balls also have drawbacks. Specifically, thread wound golf balls have relatively poor durability (cut resistance and fatigue resistance) and do not fly the same distance as solid golf balls, overall. Further, thread wound golf balls are more complicated and expensive to manufacture. Thread wound golf balls are manufactured by winding a natural or synthetic rubber thread around a liquid and/or solid center until the desired diameter is reached. To achieve the desired characteristics, numerous parameters must be controlled, such as center size and type, winding tension, thread size and thickness. As will be appreciated, it is difficult to control these parameters in the manufacturing environment. Controlling these parameters requires sophisticated winding and tensioning apparatus.
The elastic thread of the wound balls must be wound under high tension to produce a ball which will achieve high velocity. Because of this high tension, however, there is a risk of thread snap during winding and later manufacturing steps. For example, it is difficult to ensure that the wound subassembly is concentric. This requires control of the parameters outlined above, as well as the rotational position of the center.
The thread used in such golf balls is also sensitive to heat, thereby limiting the options available to apply the cover around the wound center. For example, injection molding a cover around a wound subassembly will typically cause the thread to snap during the molding process.
Accordingly, there is a need for a golf ball having the long flight and ease of manufacturability of two-piece golf ball and, at the same time, the benefits of greater control and better feel provided by a thread wound golf ball.
One aspect of the invention is a golf ball having a core, a cover, and an intermediate skin between the core and cover. The intermediate layer is a soft elastomeric material applied around the core from a liquid dispersion so that the material has substantially the same properties of elasticity and softness as said material prior to being formed over said core. Preferably, this intermediate layer is formed by dipping.
It has been determined that a golf ball having an intermediate layer of soft elastomeric material formed by dipping can provide unexpectedly improved controllability. Resulting in a solid golf ball having controllability very similar to thread wound golf balls. Specifically, the intermediate soft elastomeric layer can improve controllability by increasing the spin rate of the ball when the ball is hit with short irons. Advantageously, these benefits an be achieved while still providing the benefits of a two-piece golf ball.
Desirably, the elastomeric material may also provide a soft feel, whose effect may be adjusted by varying its thickness, hardness, and relative position from the ball surface. When the elastomeric material is applied to the core by dipping, it maintains its original properties of elasticity and softness, because the dipping technique preserves the natural chain structure of the elastomer. This is in contrast to the degrading of the structure which occurs in long kneading operations, commonly used in connection with molding and curing techniques.
By applying the intermediate layer through dipping, a very thin and homogeneous soft intermediate layer can be applied. These thin and homogeneous thicknesses are not achievable by conventional molding techniques used commonly to cover the core with a plastic layer.
Another aspect of the invention is a method of manufacturing a golf ball, including providing a core, dipping the core in a bath comprising a dispersion of elastomeric material to produce a thin layer of elastomeric material around the core, drying the layer, and molding an outer cover around the dried elastomeric layer.
Advantageously, this process permits a core to be covered with a soft rubber layer having a very small thickness. Such small thicknesses are difficult to achieve by other techniques. Advantageously, this process lends itself to a wide variety of rubber materials, and intermediate layers having different thicknesses and hardnesses.
Importantly, the process is particularly suited to economical manufacturing techniques. The system uses only low weight, low cost and low energy consuming machines.
Additionally, this technique protects the core structure from deterioration. Specifically, the core typically degrades in the presence of high temperatures. For example, high temperatures tend to reduce the restitution of the core or rebound energy of the core.
Yet another aspect of the present invention is a method of manufacturing a golf ball wherein a thin intermediate layer is formed by at least two consecutive dipping steps in different baths of elastomeric materials to produce at least two coats of soft elastomeric material around the core. Preferably, these materials have a different hardness, so that the properties of the golf ball can be precisely controlled by "blending" the characteristics of the materials in each of the two baths.